Or possibly, in Parker and Broderick's case, they tried but couldn't. Entertainment Weekly's Web site, EW.com, quoted a friend saying, "They had a lot of unsuccessful tries. They came to the conclusion that this was going to be the best alternative for expanding their family."
There's also the matter of Parker's age. Right around the mid 40s, "pregnancy with a woman's own eggs becomes very rare," said Paulson, who heads the division of reproductive endocrinology and infertility at the University of Southern California's school of medicine. "Most, if not all, may be using an egg donor."
It's the question many wonder about -- whose eggs are they?
Larry King posed the question to model Cheryl Tiegs when he interviewed her and her then-husband Rod Stryker in 2000 about the birth of their twin boys Jaden and Theo via a surrogate.
Tiegs, who was 52 at the time, said she used her own eggs.
"When we were trying to get pregnant, I produced one perfect egg, and then when we did the one with the surrogate, I had three eggs. So I don't see why that's such an impossibility, when my system is in -- still in good working order," Tiegs told King. "It's not easy. I had to have a lot of shots. But I don't see why -- it certainly is possible."
Many questioned Tiegs' claim.
"A twin pregnancy using 50-year-old eggs is a medically unprecedented event," Paulson said. "It's not impossible, but very improbable."
"I want to respect people's privacy," Paulson added. "Even if it's not medically impossible, why not grant them the element of doubt they wish to have. Do we want to have that kind of thing revealed to the children before they have had a chance to hear about it from their mother?"
"It's very personal, it's something that the family needs to discuss among themselves," Bubrick said about mothers who use egg donors. "They still have created their child. The true genesis of the child is in the hearts and minds of the couple. It is their child."
In 2003, Lunden, at the age of 54, had her first set of twins via a surrogate -- the second set arrived two years later -- but she refused to answer questions about her biological connection to them. (She also has three older daughters by a previous marriage.)
Actors and husband and wife Courtney B. Vance and Angela Bassett have said their twins, delivered by a surrogate in January 2006, are biologically theirs. They told Oprah Winfrey they went through seven years of failed fertility treatments, including IVF, before turning to the Center for Surrogate Parenting.
Age isn't the only factor standing in the way of some women having children. Some women either have a problem with their uterus or don't have one, or they have a medical condition that makes pregnancy inadvisable.
In the case of the Grammers, doctors discovered Camille had a form of Irritable Bowel Syndrome, which could present serious health risks if she attempted to give birth. So the Grammers turned to a surrogate twice to have their daughter Mason and son Jude.
"It's very sad when you hear stories of cancer, medical conditions, miscarriages, women born without a uterus," Bubrick said. "We have a lot of couples who have been hurt along the way. This is their last hope."